1. Field of the Invention
The present invention relates to a light source apparatus, an endoscope system and an operating method. More particularly, the present invention relates to a light source apparatus in which field sequential lighting and simultaneous lighting are changeable, and performance of color separation can be high typically for imaging with narrow band light, an endoscope system and an operating method.
2. Description Related to the Prior Art
An endoscope system is well-known in the field of medical diagnosis, and includes a light source apparatus, an electronic endoscope and a processing apparatus. The light source apparatus emits light for illumination to an object of interest in a body cavity. An image sensor in the endoscope images the object of interest illuminated with the light, and generates an image signal. The processing apparatus processes the image signal in image processing, and generates an image for display on a monitor display panel.
Two lighting controls are available in the endoscope system, including field sequential lighting and simultaneous lighting. In the field sequential lighting, red (R), green (G) and blue (B) light components are applied to the object of interest sequentially one after another. A monochromatic image sensor images the object of interest illuminated with the light components in sequential steps. In the simultaneous lighting, red (R), green (G) and blue (B) light components are applied to the object of interest simultaneously, so that white light is applied thereto. A multi-color image sensor for use with simultaneous lighting is used, has a color filter, and images the object of interest illuminated with the white light.
The field sequential lighting generates one image by imaging of three frames with the monochromatic image sensor, and has a feature of high spatial resolution and low time resolution. In contrast, the simultaneous lighting generates one image by imaging of one frame with the multi-color image sensor, and has a feature of high time resolution and low spatial resolution.
In short, the field sequential lighting and the simultaneous lighting have the features distinct from one another. In consideration of this, there is a type of the endoscope system as disclosed in JP-A 2002-209839 in which first and second endoscopes are selectively usable. The first endoscope has the monochromatic image sensor. The second endoscope has the multi-color image sensor. Any one of the first and second endoscopes is connected to the light source apparatus and the processing apparatus. The endoscope system is switchable to set the field sequential lighting upon connecting the first endoscope, and to set the simultaneous lighting upon connecting the second endoscope.
Examples of the multi-color image sensor include a three primary color image sensor or first multi-color image sensor with a three primary color separation filter (of red, green and blue), and a complementary color image sensor or second multi-color image sensor with a complementary color separation filter (of yellow, magenta and cyan). The three primary color image sensor has a lower sensitivity than the complementary color image sensor, but has a better performance of color reproduction than the complementary color image sensor, and is typically used in the endoscope system with higher importance in the color. The three primary color image sensor has a poorer performance of color reproduction than the complementary color image sensor, but has a higher sensitivity than the complementary color image sensor, and is typically used in the endoscope system with higher importance in the sensitivity.
In addition to the normal imaging with white light in the endoscope system, there is a method of narrow band imaging mode in which narrow band light with a narrow wavelength range is used for imaging. The narrow band imaging mode is characterized in imaging the object of interest with surface blood vessels in body tissue with good visual recognition in contrast with normal imaging in which the surface blood vessels with may not be recognized in optical information. It is possible in the narrow band imaging mode to diagnose progress of a lesion in the surface blood vessels, penetration depth of the lesion and the like by sharply imaging the surface blood vessels.
In the narrow band imaging mode, narrow band blue light and narrow band green light are used as light components easily absorbable in hemoglobin in blood. The narrow band blue light has a center wavelength of approximately 415 nm. The narrow band green light has a center wavelength of approximately 540 nm. Furthermore, there are two lighting controls in the narrow band imaging mode, including the field sequential lighting in combination with the monochromatic image sensor, and the simultaneous lighting in combination with the multi-color image sensor, as disclosed in U.S. Pat. No. 8,531,512 (corresponding to JP-B 4009626).
In the narrow band imaging mode of the endoscope system, the narrow band blue light and the narrow band green light are detected discretely by blue and green pixels in the three primary color image sensor. It is possible to obtain an image with good visual recognition of the surface blood vessels, namely, contrast between the surface blood vessels and mucosa, owing to distinct color separation. However, the complementary color image sensor detects the narrow band blue light and the narrow band green light simultaneously with common pixels, so that color mixture occurs. There is a problem in that visual recognition of the surface blood vessels may be poor due to low performance in the color separation.